NANOSCALE THEORY, MODELLING AND COMPUTATION

The research activities in the thematic area of nanoscale theory modelling and
computation are aimed at developing theoretical and computational methodologies as well as
their implementation in the related high performance computing software, to model and
predict phenomena and experiments of systems at the nanoscale. These include
first-principles approaches for molecules, small nanoparticles and materials; atomistic and
coarse-grained molecular dynamics simulations for (bio)molecules; density functional theory
approaches to study electronic, optical and magnetic properties of nanosystems and
molecules; novel theoretical approaches to simulate the real time evolution of molecules
interacting with plasmons and light; effective-mass schemes to handle complex nanostructures
that are beyond the reach of first-principles tools. The impact of these methodologies ranges
across various applications spanning from medicine to energy conversion, quantum optics and
telecommunication, optical sensing and molecular spintronics.

1. Developments of advanced DFT methodologies. DFT has been http://intranet.nano.cnr.it/webpagine/index.php?opt=edit&id=268
extended to include the description of additional quantum states by introducing advanced
functional forms. Recent theoretical developments have demonstrated that starting from
standard results of first-principles simulations, it is possible to derive two estimators, namely
aplasmonicity index and a “natural” metric distance of electronic correlations, to quantify the
plasmonic character of optical excitations in nanostructures and the internal correlationsin
different materials, respectively.

The distance, Dx, is computed between atoms
with atomic numbers Z and Z-1 and is plotted against Z for the s and p blocks of the periodic
table. The curve peaks when considering the last atom of one row and the first of the next.
The expected periodicity is well reflected in the behaviors of Dx.S. Marocchi, S.
Pittalis, and I. D'Amico Fermionic correlations as metric
distances: A useful tool for materials science, Phys. Rev. Materials, 1, 043801
(2017)

2. Electronic, Magnetic, and Optical Properties. Novel ab-initio
modeling for the optical time resolved experiments applied to low dimensional systems, have
revealed the importance of many body effect even in the low pumping regime. Ab initio
ground and excited-state calculations are able to clarify the role of quantum confinement
effect and of the surface orientation, in anatase nanosheets. Large scale DFT simulations have
captured the microscopic mechanisms behind the magnetic coupling between magnetic
molecules and substrate, and have suggested possible switching mechanisms, a key element in
the realization of functional molecular magnetic devices.

Top left panel: a cartoon of the corrugated graphene as given by the egg-box model. Bottom left panels: C1s core-level shifts (CLS) computed for the two non-equivalent C atoms of Gr@Co(0001) in top-fcc registry (C atoms at fcc-hollow and on-top sites), with increasing graphene-Co distance and represented as Lorentzian functions with a width of 0.1 eV. The average of the CLS computed for GR@top-fcc at 2.05 Ang distance was used as reference, here set to zero. Aside: top view of the studied fcc-top Gr@Co(0001) geometry with grey representing C and blue Co atoms. The top Co layer is represented in lighter blue. The 1x1 unit cell is reported. Circle and triangle symbols refer to fcc and top adsorption sites, respectively. Diamond symbols correspond to the hcp site.

Right panels:(a) Core-hole shift dependence with C-Co distance computed for Gr@Co. The red line gives the average of the values computed for the two non-equivalent C sites of four different registries of commensurate Gr@Co, shown by the symbols in different colours. (b) Height distribution for corrugated Gr@Co as given by the egg-box model. (c) XPS spectra computed as a sum of Lorentzian functions centred in the core-hole energies given in the left panel. (d) Experimental C1s XPS spectra.
G. Avvisati, S. Lisi, P. Gargiani, A. Della Pia, O. De Luca, D. Pacile, C. Cardoso, D. Varsano, D. Prezzi, A. Ferretti, and M.G. Betti, FePc adsorption on the moiré superstructure of graphene intercalated with a Co layer, J. Phys. Chem. C , 121, 1639
(2017)

4. Coarse-Grained Force Fields. Computational modeling of the
membrane penetration mechanisms by peptide-aggregate could be greatly facilitated by using
simplified coarse grain (CG) models. Recent strategy have been developed to build and
optimize statistics based analytical CG force fields, particularly suited to account for the
common interaction motives between biopolymers.

Development of a specific Coarse Grained approach to achieve an accurate description of protein-surface systems. The novelty of the research proposal respect to the state-of-the-art, is the description and parameterization of protein-NP interaction based on data obtained from docking and enhanced sampling molecular dynamics including information about the diffusivity of the gold NPs and protein in solution.V. Tozzini, G. Brancolini, Multi-Scale Modeling of Proteins interaction with Functionalized Nanoparticles, Current Opinion in Colloid & Interface Science (2018).